The mammalian Cks (Cks1 and Cks2) proteins are small molecular weight ( about 9kDa) proteins that are highly related evolutionarily to the yeast S. cerevisiae CKS1 pombe suc1+ gene products (both about 13 kDa) which interact with the cyclin dependent kinases (cdks). The yeast genes have been shown to be essential for survival, but the exact biologic function of either yeast protein or the mammalian proteins has not been determined. In addition, it is known that the two human protein are encoded by separate, and distinct, gene loci. The necessity of two separate gene products in humans is also not clear. The Principal Investigator originally identified the S. cerevisiae Cks gene as a high copy number suppressor of temperature-sensitive S. pombe cdc2 and S. cerevisiae cdc28 mutations, the human isoforms, and published a number of structural and genetic studies regarding these proteins. The studies in this proposal are focused on determined the functional relationship between the tow mammalian isoforms as well as examining possible role of these proteins in human disease. To do this several strategies will be used to complement existing data: (1) antisense experiment are proposed to assess the phenotypic consequences of eliminating the function of Cks isoforms in cells in tissue culture, individually and together; (2) in parallel, Cks gene knockout in mice will be created to investigate the role (s) and essential nature of Cks protein (s) during developing development; (3) both two-hybrid and biochemical studies will be employed t identify downstream targets of the Cks proteins; and (4) the human Cks genes will be mapped to chromosomal loci as a first step in determining whether disruption of their function genetically might be associated with human disease.